1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium and, in particular, to an improved magnetoresistive read transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material as a function of the amount and direction of magnetic flux being sensed by the element.
The prior art also teaches that in order for an MR element to operate optimally, two bias fields should be provided. In order to bias the material so that its response to a flux field is linear, a transverse bias field is generally provided. This bias field is normal to the plane of the magnetic media and parallel to the surface of the planar MR element.
The other bias field which is usually employed with MR elements is referred to in the art as the longitudinal bias field which extends parallel to the surface of the magnetic media and parallel to the lengthwise direction of the MR element. The function of the longitudinal bias field is to suppress Barkhausen noise which originates from multi-domain activities in the MR element.
Magnetostriction has been used to stabilize the read back signal of thin film inductive heads. U.S. Pat. No. 4,242,710 teaches that the composition of the pole tip and yoke material are tailored and controlled to have a proper magnetostriction coefficient, and that negative magnetostriction is best for pole pieces for thin film inductive heads.
U.S. Pat. No. 4,626,947 teaches that the characteristics of the thin film magnetic head depend on the magnitude of the magnetostriction rather than the sign and for this reason the magnetostriction coefficient should be limited to no more than 6.times.10.sup.-7. U.S. Pat. No. 4,750,072 discloses a thin film magnetic head in which the central part of the magnetic core is formed of a material having a positive magnetostriction and some side parts of the magnetic core have a negative magnetostriction to prevent the formation of edge domains.
U.S. Pat. No. 4,663,607 discusses the magnetostriction requirements of an MR element, and states that the MR element should have zero magnetostriction so that variations in composition of the MR element prevent magnetic characteristics from changing. Since it is difficult to produce a zero magnetostriction in a single layer due to manufacturing tolerances, a structure is utilized which has multiple layers with the layers alternating with a positive magnetostriction of a particlular magnitude and a negative magnetostriction of the same magnitude. The manufacturing tolerance for the multiple layers tend to cancel so that a composite film having a magnetostriction very close to zero results.
Common practice in the art has been to have a soft magnetic bias layer with a magnetostriction close to zero. However, the prior art does not discuss the effects of the use of high magnetostriction materials on the bias profile of MR sensors.